The present invention is concerned with improvements in or relating to an electrical heating molded-element or unit comprising inorganic fibers and adapted for use in the wall of an electric furnace or the like.
Fibrous molded blocks comprising heat-resistant inorganic fibers added with minor amounts of binders have recently been used in the wall of an electric furnace or the like in place of brick. In addition, an electrical heating molded-element has been put to practical use, which is manufactured by embedding or confining a heating wire in one side of such a block.
The above-mentioned molded-element comprising inorganic fibers is light in weight and excels in heat insulation. Further, the electrical heating molded-element having a heat wire embedded in its one side has the advantage that it requires no specially designed means for supporting the heating wire, and is characterized in that it is safer to use due to the fact that the heating wire is not exposed to the outside. However, the heating element of this type is disadvantageous in that the heat conduction occurring from the embedded heating wire to the inside of an electric furnace through the fibrous layer is limited thanks to the good heat insulation of inorganic fibers. Another problems results from the fact that the temperature of a portion of the heating element around the heating wire is markedly higher than that in the furnace during use. This causes premature deterioration or degradation of said portion. Still another problems arises due to the low strength of the fibrous molded-element; in some cases, the molded-element may locally disintegrate with the expansion and contraction of the heating wire.